This invention relates to digital filters, and in particular to a digital notch (band stop) filter that is capable of monitoring the skirts of the signal it is rejecting and readjusting itself to maintain the desired residue in the passband. Previously, adjustable notch filters were adjusted on the basis of open loop calculations, by additional pieces of equipment designed to measure the leakage (i.e., a bandpass filter adjacent to the notch filter), or by noting that leakage is interfering with the following processing steps. Such methods of course add substantial cost and complexity to systems using filters of this type.
There currently exists, therefore, the need for simplified inexpensive self-adjusting digital filters. The present invention is directed toward satisfying this need.